The focus of this project is (1) to develop methods to evaluate the risks from a hazardous waste disposal site and (2) to assess the feasibility of mitigating those risks using either native soil microorganisms or bacteria with specific biodegradative traits. Our hypothesis is that a waste site is a dynamic system which presents evolving risks. These changing risks to organisms located near the site are a function of the movement of toxic chemicals within and off the site, chemical and microbiologically catalyzed transformation of waste materials, and toxicant interactions based on exposures to multiple chemicals. Understanding the changes occurring within this system may lead to the design of remediation strategies for the most hazardous materials at a particular site. The chemicals chosen for study are the chlorinated hydrocarbons and toxic metals. A number of chlorinated hydrocarbons were heavily employed as solvents for decades before their toxic (e.g., carcinogenic) properties were established. They were frequently disposed of improperly, and, as a consequence, they are among the most widespread and potentially dangerous environmental contaminants. Because chlorinated hydrocarbons consist of carbon, hydrogen, and chlorine, techniques can be envisioned which can completely mineralize them to carbon dioxide, water, and chloride ion. Metals represent a much different environmental problem. Although the chemical and physical form of the metal is subject to manipulation, metals cannot be destroyed. Their toxicity is more difficult to evaluate because slow elimination from organisms permits metals to accumulate in living tissue. Consequently, metals represent a vastly different kind of challenge to both risk assessment and remediation efforts.